Interpretive Summary: Breeding status and buck age affect the sex ratio of offspring from White Tail deer bucks to deviate from an expected 50:50 (males: females). The purpose of this experiment was to determine if the sex ratio of offspring produced by bucks of different ages and breeding status was related to the ratio of X- and Y-sperm from semen collected at 2 time points during the rut. Semen was collected from 19 captive male white-tailed deer housed at the Mississippi State University Deer Pens on 16-17 October 2000 and 14 of the same bucks on 5 February 2001. The relative DNA content of sperm bearing the X- and Y- sex chromosomes and their distribution in ejaculates was determined using DNA fluorescence flow cytometry. The ratio of X- and Y-sperm (50.1: 49.9) did not differ significantly from a 50:50 ratio and did not differ between deer or collection period for the 33 ejaculates evaluated. The X- to Y-sperm ratio remained the same regardless of reproductive effort. Therefore, altered offspring sex ratios in cervids are most likely due to changes with female reproductive physiology.

Technical Abstract:
The primary sex ratio of the family Cervidae may vary at conception and/or birth from an expected 50:50 (males:females). Fertilization by X- or Y- chromosome-bearing sperm (referred to simply as X- and Y- sperm) ultimately controls the sex of offspring; however, alteration of the fetal sex ratio could occur at different points of the reproductive process. The purpose of this experiment was to determine if the sex ratio of offspring produced by bucks of different ages and breeding status was related to the ratio of X- and Y-sperm from semen collected at 2 time points during the rut. Semen was collected from 19 captive male white-tailed deer housed at the Mississippi State University Deer Pens on 16-17 October 2000 and 14 of the same bucks on 5 February 2001. The relative DNA content of sperm bearing the X- and Y- sex chromosomes and their distribution in ejaculates was determined using DNA fluorescence flow cytometry. The ratio of X- and Y-sperm (50.1: 49.9) did not differ significantly from a 50:50 ratio and did not differ between deer or collection period for the 33 ejaculates evaluated. The X- to Y-sperm ratio remained the same regardless of reproductive effort. Therefore, altered offspring sex ratios in cervids are most likely due to changes with female reproductive physiology.